1. Field of the Invention
The present invention relates to a shaft seal mechanism appropriately used for a rotating shaft or the like of a large size fluid machine, such as a gas turbine, steam turbine, compressor, water turbine, refrigerator, pump or the like.
2. Description of the Prior Art
Generally, around a rotating shaft of a gas turbine, steam turbine or the like, a shaft seal mechanism is provided for reducing leakage of working fluid leaking to a lower pressure side from a higher pressure side. As one example of such a shaft seal mechanism, a leaf seal shown in the Japanese laid-open patent application 2002-13647, for example, is known.
FIG. 6 is a cross sectional view of one example of a prior art leaf seal (shaft seal mechanism) of the kind mentioned above, wherein this leaf seal is seen on a cross section including an axis of a rotating shaft. In FIG. 6, numeral 1 designates a leaf seal and numeral 2 a rotating shaft. The leaf seal 1 is constructed such that a plurality of thin plates 3 of a flat shape having a predetermined size of a plate width in an axial direction of the rotating shaft 2 are arranged in layers in which a minute gap is provided between each of the thin plates 3 in a circumferential direction of the rotating shaft 2 so that a thin plate assembly 9 of an annular shape is formed. These thin plates 3 have their outer circumferential proximal end side fixed to a split housing or leaf seal ring 5 (5a, 5b) via a brazed portion 4 and their inner circumferential distal end side arranged inclinedly with an acute angle relative to an outer circumferential surface of the rotating shaft 2 so as to make a slidable contact with the outer circumferential surface of the rotating shaft 2 by a pre-load. It is to be noted that, when seen on a plan view, each of the thin plates 3 has a T-shape in which the size of width w1 of the above-mentioned outer circumferential proximal end side is larger than the size of width w2 of the above-mentioned inner circumferential distal end side.
By the construction mentioned above, the thin plates 3 seal the outer circumferential surface of the rotating shaft 2 and thereby an annular space formed around the rotating shaft 2 is divided into a higher pressure side area and a lower pressure side area. Also, the leaf seal ring 5 comprises a higher pressure side side plate 7 on the side opposed to the higher pressure side area and a lower pressure side side plate 8 on the side opposed to the lower pressure side area so that the thin plates 3 are fitted in between the higher pressure side side plate 7 and the lower pressure side side plate 8. The respective side plates 7, 8 are arranged also to function as a guide plate for guiding a direction to which pressure acts.
In the leaf seal 1 constructed as mentioned above, when the rotating shaft 2 rotates, a dynamic pressure effect is caused by the rotation of the rotating shaft 2 and the distal end of each of the thin plates 3 is levitated from the outer circumferential surface of the rotating shaft 2 so that contact of the distal ends of the thin plates 3 with the rotating shaft 2 is avoided. Thereby, abrasion of the thin plates 3 is avoided and the seal life is elongated.
While the prior art leaf seal 1 is manufactured such that each of the thin plates 3 is fitted in between the two split housings 5a, 5b and the jointing portion between the housings 5a, 5b is fixed by welding or bolting, there are many kinds of rotor diameter sizes, different from each other, according to the places where the leaf seal is to be provided. Thus, in the manufacture of the housings 5a, 5b, it is necessary to individually prepare exclusive jigs according to the diameter sizes. As the leaf seal 1 is used in various places and the diameter sizes are mostly different from each other, to prepare such exclusive jigs is a large obstruction in reducing the manufacturing cost.